In a general mechanical manufacturing area such as a micro electro discharge manufacturing (micro EDM) area, it is necessary to use a wire electro discharge grounding (WEDG) technique and a numerical control (NC) program to manufacture the micro spherical electrode tool.
The micro spherical stylus for EDM process comprises two portions, one is a circular-shaped electrode and the other portion is a micro sphere. In general, the micro spherical stylus is made by machining the surface contour of a metal rod to form the circular-shaped electrode and the micro sphere. When the EDM machine and NC program are utilized to manufacture the micro spherical stylus, the obvious electro discharge craters will be left on the surface of the micro sphere after the micro spherical stylus is formed. Further, since this conventional micro-tool fabrication shapes the surface contour of the circular-shaped electrode and the micro sphere. When the diameter of the micro sphere is less than 0.1 mm, the manufacture of the micro spherical stylus will involve a high level of challenge and difficulty. Particularly, the electro discharge craters will affect the measuring accuracy of the micro coordinate measuring machine, and thus this conventional method is not suitable for manufacturing micro spherical styluses for micro coordinate measuring machines.
There are other conventional manufacturing methods to fabricate the micro spherical stylus such as, melting a front end of a glass fiber thread (having a diameter of 0.125 mm) by using a hot melting method to form a small spherical optical glass fiber stylus, but the spherical stylus formed by the hot melting method usually has a diameter much greater than 0.125 mm. Since the optical glass fiber comes with a soft and flexible feature, the formed stylus is bent or curled easily when the stylus is in contact with an object during the measuring process. Obviously, this method is also not suitable for manufacturing a micro sensor head of the micro coordinate measuring machine.
Although those traditional micro-EDM manufacturing machine can be used for manufacturing various types of micro rod styluses made of a hard material such as, a super hard alloy tungsten carbide (WC) or a pure tungsten material, yet the manufacture of micro spherical styluses for micro coordinate measuring machines cannot be achieved due to the traditional methods cannot fabricate smaller diameter of micro spherical stylus. Further, if the required micro electrode tool is manufactured by modifying the circular rod material having a larger diameter (ψ over 0.5 mm), the manufacturing time will be extended tremendously.
Another traditional method is to use a micro electrode tool that is currently available in the market to manufacture the micro spherical stylus. Once a correct size of micro electrode tool is selected, a micro sphere (such as a micro metal sphere or a micro glass sphere) is then adhered to a front end of the tool to form the micro spherical stylus. The fabrication process of this method involves two separated steps, first, selecting the right size of micro electrode tool to be used, and then adhering the clamped micro sphere to the front end of the micro electrode tool to form the micro spherical stylus. Since the issue of clamping the micro sphere by a clamp can cause a deviation of the micro spherical stylus easily, therefore the micro sphere is deviated from the axis of the tool. Furthermore, the electrode tool may be bent or broken easily during the clamping and gluing processes when the diameter of the electrode tool is smaller than 0.1 mm.
As described above, the micro spherical stylus tip head for micro coordinate measuring machines presently undergoes extensive researches and developments in measuring centers all over the world, and traditional machining process using the optical glass fiber hot melting method for the manufacture of micro spherical styluses still have many problems, and are not suitable for manufacturing the micro spherical styli tip of the micro coordinate measuring machines, and thus the micro coordinate measuring machine (Micro CMM) cannot be used for measuring physical dimensions and the profile of components or sub-micron components of the micro semiconductor fabrication process due to the size limitation of the micro sensor head.
It is a major subject of the invention to develop a micro spherical stylus manufacturing machine for forming a micro electrode tool on the same machine platform, and then forming a micro spherical stylus for the micro coordinate measuring machine by a gluing process.